Piston engines, such as a four-stroke, normally aspirated piston engine, achieve 100% volumetric efficiency when the volume of air or fuel/air mixture, at atmospheric pressure, taken into the combustion chamber is equal to the volume of the combustion chamber. Street vehicles customarily achieve a volumetric efficiency of about 70 to 90%, while high performance or racing engines will operate between 90% and 120%. Increasing volumetric efficiency increases the volume of the fuel/air mixture being ignited in the combustion chamber and, consequently, the power output of the engine goes up. One way to increase the volumetric efficiency is with turbo charging, whereby the pressure at the intake manifold is increased so that a greater mass of air or fuel/air mixture is received into the combustion chamber. Another way engine designers have sought to increase volumetric efficiency is to tune the intake manifold or tubes. That is, by varying the length and taper of the intake tubes, resistance and acoustic losses to air flow through the tube can be lessened. Improvements are continually being sought by engine developers.